The invention relates to a method of removing undesired particles from a surface of a substrate, in which a removing force is exerted on the particles by means of a liquid.
Such a method is particularly suitable for removing undesired particles from a surface of a semiconductor substrate.
In the manufacture of integrated circuits (IC's), a substantial part of the rejected IC's is due to the unfavourable influence of particles which have adhered to the substrate in one of the processing steps. During the ultimate operation of the IC, these particles may give rise to instabilities, voltage breakdowns or shortcircuits, which render the whole IC unserviceable. During the manufacture of IC's, about 60% of the rejected IC's is due to such a contamination by small particles, so that removal of these particles is an important factor for the production yield.
U.S. Pat. No. 4,118,649 discloses a method of the kind mentioned in the opening paragraph, in which the force removing the particles is produced by megasonic waves. In this case, the substrate is located in a tank containing a cleaning liquid, in which megasonic waves are generated. The frequency of these waves is 0.2 to 5 MHz. Particles having a diameter of about 0.3 .mu.m and larger can be effectively removed from the surface of the substrate.
The known method described has the disadvantage that the removal of the particles requires expensive and complicated equipment and that particles having a diameter smaller than about 0.3 .mu.m cannot be effectively removed from the surface of the substrate.
Particles having a diameter of more than 10 to 20% of the minimum detail size in the IC can give rise to an ultimately unsatisfactory operation of the IC. This means that in the modern large-scale integration of components in IC's, in which details of the order of magnitude of 1 .mu.m occur, particles having a diameter smaller than 0.3 .mu.m can exert a destructive influence. Since the scale on which components are integrated in IC's is gradually on the increase, the unfavourable influence of particles having a diameter of 0.3 .mu.m and smaller will in the future play an increasingly important part.